In certain wooden building structures, tie-down systems are utilized to provide increased strength and stability, particularly to counteract severe wind and earthquake loads. Examples of such systems are shown in U.S. Pat. Nos. 4,875,314 and 4,321,776. In order for such tie-down systems to function with maximum effectiveness, the tie rod connections must be kept snug and tight, so that there is no excess "play" or looseness. Wooden members have a natural tendency to shrink with age. Therefore, although a tie-rod hold down system may be tight and snug when installed, wood shrinkage may cause tie rod connections to loosen with the passage of time. It is impractical and expensive to provide access to all conventional fasteners of a tie-rod system so that they can be manually tightened at selected time intervals. Therefore, it is essential to counteract the looseness in such connections that tends to develop and to provide some means for automatically maintaining the snugness of tie-rod connections in a structural tie-down system during the life of the building for which the system is used. The present invention solves this problem.